Small diameter tubular devices have been found to provide critical advantages in numerous and varied industrial applications. These applications range from catheters and stents in the medical industry to tubular capacitors in the electronics industry. For example, tubular devices, such as Pi capacitors, are well known devices used in RFI (radio frequency interference) and EMI (electromagnetic interference) filters for high frequency applications. Typically, the capacitors are composed of various electronics grade ceramic compositions that have a wide range of electrical properties, which include, but are not limited to, “K” (dielectric constant) and “TC” (temperature coefficient). These basic tubular forms, referred to as the dielectric, are manufactured using various conventional manufacturing processes.
In one method, the capacitor is subjected to the application of a thick film conductor (i.e. electrode), typically in the form of a mixture of silver, glass frit, and organic binders, by mechanical or dipping methods. The thick film material is applied from each end of the axis onto the wall of the inside diameter to, typically, a distance shorter than the center point of the axial length. In this method, the thick film material is coated on the interior substrate of the capacitor to slightly less than half the length from each end of the capacitor. Accordingly, the wall of the interior substrate at or about the center of the axial length is void of the thick film conductor material, which provides electrical insulation between the two inside electrodes. The device is then coated on the surface of the outside diameter with a thick film conductor to form the ground electrode and is, thereafter, subjected to a drying and sintering process to bond the thick film conductors to the device.
It is well recognized that forming small diameter tubular devices, such as by the method described above, is both time consuming and labor intensive. For example, the prior art method set forth above is generally effective in forming a two electrode capacitor, but requires significant allocations of time and manpower to do so. In addition, this method provides the formation of Pi (i.e., two electrode-containing) capacitors used in the electronics industry, but offers limited or no manufacturing flexibility in other electronics applications or applications in other industries. Even with automation, the cycle time for coating each tubular device employing conventional methods is relatively slow. Typical dimensional variations of the tubular devices also affect the yield and quality output from the prior art methods.
In light of these drawbacks, there is a need to manufacture tubular devices, such as tubular capacitors, in a more cost-effective manner and by methods that provide greater manufacturing flexibility, such that one or more annular bands may be formed on the interior substrate with greater speed and accuracy, which allows for a greater product output and reduced manufacturing cost.